Wave Velocity Ratio Variation of Hebei Zanhuang Earthquake Swarm

To calculate the velocity ratio of the Zanhuang earthquake swarm in Hebei province, we picked up the travel time information of P wave and S wave from seismic phase observation data recorded by 5 fixed seismic station and two other temporary stations. The results show that the velocity ratio changing range is little larger around the M_L3.2 mainshock on June 3rd, 2015 than the average changing range of -0.04-0.04; The velocity ratio of the earthquake swarm went through a process of low value anomaly rebounding-decreasing-rapid recovery-decreasing.